REACTION OF SILYLCOBALT TETRACARBONYLS WITH OXIRANES - KINETICS AND MECHANISM

It has been shown that (beta-silyloxyacyl)cobalt tetracarbonyls are fo rmed in the reaction between silylcobalt tetracarbonyl, terminal oxira ne, and carbon monoxide. The linear acyl isomer is obtained with a reg ioselectivity of about 80%, which is practically independent of the na ture of the substituents in the silyl group. Kinetic studies have reve aled a first order dependence on Ph3SiCo(CO)4, an increasing order wit h respect to ethyloxirane, and zero order with respect to [Co(CO)4]- a nd CO. A mechanism involving a rapid formation of a tight ion pair, ra te-determining internal S(N)2 type substitution, and fast insertion of CO is suggested.